YJM Boost Problem?

[ufguy73]

Hey guys - I posted this on another forum but thought there is so much knowledge here I would try my luck twice!

Just recently received my second (let the first one foolishly go) YJM head and am loving it - BUT, there is definitely something up with my Boost. Even with the NG not engaged I will be playing at volume and all of a sudden my volume will drop in half for a little while and then come back to full volume again.

it is almost like maybe there is an incomplete connection or join somewhere - I dont suppose there is any chance that a particular preamp tube position is responsible solely for the Boost? I dont know if it's a tube though because the amp seems to work perfectly fine when the Boost is not engaged...but in some ways I was hoping maybe it could be as easy as a preamp tube swap or something.

incidentally, i did run the autobias for the correct range when i first received the amp - i thought i was through the woods since there was no problem with the procedure, which i know others have suffered from...but i guess i was happy too soon!

[surfnorthwest]

There is no tube that controls the booster, the booster is all solid state. The fourth preamp tube on the YJM is for the noise gate and reverb so you won't lose volume when engaged.

Are you running any other pedals (front or loop) when this happens?

[ufguy73]

no other pedals, just the yjm and built-in boost

[snark]

Give me your exact settings on all controls and I will try to replicate on one of my YJMs if you like ...hope we can trouble shoot this for you

[Papus]

Inconsistent power affects the attennuator

[Soulcaster]

I think it sounds like a dodgy tube....take it back. Tubes have a 30 day or 3 month warranty if I remember correctly.

[ufguy73]

Give me your exact settings on all controls and I will try to replicate on one of my YJMs if you like ...hope we can trouble shoot this for you

thanks a lot!

wouldn't you know, ive had a hell of a time getting the issue to surface again. Today, instead of an overall lowering of volume, i was exepriencing a sort of jagged decay of single lead notes (almost like a cutting in-and-out static type thing).

I basically had everything dimed - no jumpering, lead I volume on full, all tone controls on full, NG off and Boost volume and gain on full. I was also using the bridge pickup on an R9 LP with volume and tone on full. I can't say I would actually use these settings but since I just received the amp I was doing a lot of playing around and once I found this issue I sort of tried to hone in on it.

someone posted something to me on another forum:

'what happens over there with the boost (you dimed it right?) sounds very much like a phenomenon called blocking distortion...
the signal into one of the tube gain stages is probably too high, so its control grid becomes so positive that it starts to draw current... electrons being emitted by the cathode can't reach the plate (anode) anymore, as the control grid is sucking them up... pretty much the gain stage starts acting like a diode instead of a triode and the signal is "walking into a dead end" for a split second...
it is not something that you can call faulty, you simply put too much signal into that stage, which can be caused by either too much gain provided by the boost and/or high output pickups

it happened to me as well with the AFD100... just dial the boost a bit back and you should be OK '

has anyone else had problems when diming the amp volume and Boost volume and gain knobs??